The invention relates to an apparatus for measuring the steering angle of a steerable wheel of a vehicle.
In order to determine the castor, the kingpin inclination and the track differential angle in a vehicle it is necessary to measure the steering angle of the steerable wheels of said vehicle. The castor is understood to be the inclination of the kingpin and/or the wheel leg axis, respectively, as compared to an imaginative perpendicular line intersecting the center of the wheel. The castor is calculated out of the changes in angles of the slope, i.e. of the angle of inclination of the wheels with respect to a perpendicular plane, between the steering angles of the wheels, at a wheel angle of 20 degrees of the left-hand wheel and a wheel steering of 20 degrees of the right-hand wheel. The kingpin inclination is understood to mean the angle at which the kingpin is inclined to the inside with respect to the line perpendicular to the transverse axis of the vehicle. The measurement of the kingpin inclination as well as that of the castor is effected at a wheel angle of 20 degrees to the left. The track differential angle is the angle between the curve-inner and the curve-outer wheel in a curve and it is measured at a steering of 20 degrees of the curve-inner wheel. For determining these parameters of the wheel suspension, it is thus necessary to measure the steering angle of the steerable wheels. Finally, the manufacturers of vehicles lately claim that the maximal steering which depends on the turning circle of a vehicle can also be measured.
For this purpose it must be possible to acquire an angle measuring range of up to 60 degrees.
From the West German patent publication 26 50 577 an apparatus is known for measuring the steering angle of steerable wheels, said apparatus comprising a reference portion to be fixed to the wheel and having a scale, and a pivoted arm being rotatably connected to the reference portion, rotatable about an axis being essentially vertical and being arranged independently from the summit of the wheel steering angle. Therein the scale at the reference portion and the pivoted arm are mutually shiftable and comprise oppositely arranged read-out devices for the pivot angle. At the reference portion, a parallel guidance is provided comprising a projector for generating a light beam, a mirror for reflecting said light beam and a screen at the projector, on which screen the reflected beam will impinge in case of a corresponding alignment of the projector and the mirror. Therein the projector is arranged on the pivoted arm, whereas the mirror is adjusted stationary with respect to the steering wheel. Said apparatus is comparatively expensive because the projector, cannot be easily handled for the required adjusting of the mirror and is not suitable for an electronical evalution of the measurement results.